Such methods and devices for reconstructing and representing multidimensional objects from one-dimensional or two-dimensional image data are especially known for reconstructing and representing three-dimensional or four-dimensional volumes from ultrasound images with position data, with an ultrasound transmitter emitting ultrasound waves onto an object and an ultrasound receiver receiving the ultrasound waves reflected from the object. To record the object the ultrasound transmitter or the ultrasound receiver is moved along the object or rotated relatively to the object while individual partial image areas of the object are recorded. Such partial image areas normally correspond to a line-by-line scanning operation (one- or two-dimensional recordings), recording the object line-by-line along a recording direction into which the ultrasound transmitter or the ultrasound receiver is moved. In known ultrasound devices, the images generated in the ultrasound device can further be used digitally or via a video outlet in a post-processing device or in a data processing system. There, the images can be stored or also directly post-processed. Said images are one- or two-dimensional images which, mostly together with their respective position, are available as one- or two-dimensional image data.
During the scanning operation the object to be examined is recorded line-by-line, i.e. individual, mainly parallel lines and “layers” or rotationally symmetric “slices” of the objects are stressed by ultrasound waves and the respective reflected ultrasound waves are received in the ultrasound device. The received ultrasound waves generate image information providing information about the individual layers or slices of the object, i.e. information about where the object for example has less or more densified material areas (e.g. cavities or boundary layers between tissue and liquid).
The individual layers or slices of the object are “piled up” or “strung together” in a data processing system in order to obtain e.g. a three-dimensional representation of the object on the display apparatus. The varying distances of different areas of a layer, i.e. the position of cavities or stronger densified material areas of the object relative to the ultrasound device are obtained by the evaluation of the grey-value information of each layer.
The known methods like e.g. ultrasound methods use a grey-tone grade (threshold) which is either predefined or must still be calculated so as to find contours in the image. The contour information is then stored in an image and, after evaluation of the distances between the ultrasound device or the ultrasound head and the outer contours of the object to be examined, generates a multidimensional image effect. The whole scanning operation spans across a specific area, e.g. the human body, wherein individual layers or slices of the object to be examined are successively recorded line-by-line within the body during the scanning operation. The individual ultrasound images are joined together spatially correct in a subsequent processing step so that the “piling up” of the individual images results in a complete three- or multidimensional image of the object.
These spatial tomographic recording methods of human organs are e.g. known from U.S. Pat. No. 5,105,819 or U.S. Pat. No. 5,159,931. According thereto, in transoesophagic echocardiography, a pivoted endoscopic probe is introduced through the patient's gullet. The ultrasonic detector is integrated in the tip as so-called “phased array”. The ultrasound head is thereby either linearly moved or rotated at the tip of the probe so that one layer of the organ is scanned from each angle setting of the rotating ultrasound head or from any displaced position of the probe. One image sequence per layer is recorded, that is to say e.g. one or more motion cycles of the organ, like e.g. a cardiac cycle. After such a sequence has been recorded, the ultrasound head when rotated about a desired angle increment by means of a motor, like e.g. a step or linear motor, is turned further or displaced by hand or linearly displaced during the linear displacement. A data processing system releases the next recording sequence wherein the data processing system can process both the data of the electrocardiogram (ECG) and the breathing and thorax motion (respiratory record).
It is further known to determine the position of the ultrasound head in any location in space during the recording by means of a position sensor. Said position sensor is located at the ultrasound head and is e.g. connected via an electromagnetic field with the data processing systems in such a way that it captures all translatory and rotary degrees of freedom so that the position, direction of motion and speed of the head can always be captured. The recorded one- or two-dimensional images can then later be spatially assigned and the recorded three-dimensional or multidimensional volume can be reconstructed.
The one- or two-dimensional images (e.g. grey-value images in ultrasound recordings) and their respective absolute position in space and/or respective relative position of the individual images with respect to each other result together with the images themselves in the one- or two-dimensional image data by means of which multidimensional objects can be multidimensionally reconstructed. Especially in clinical practice during the recording of ultrasound images it has proven itself to link the recording sequence with the ECG so that each image of a sequence is always recorded at a special phase point during the heartbeat cycle. Thus sequences of three-dimensional images can be generated in moved objects moved or organs inside creatures, which, when strung together, result in a temporarily independent three-dimensional representation of the organ. The motion of the organ can then be watched like a “film”, that is to say four-dimensionally.
Conventional methods for reconstructing multidimensional objects from one- or two-dimensional image data generally use the one- or two-dimensional partial image areas, pile them up one after the other in accordance with the respective positions and interpolate the “missing data” between the individual one- or two-dimensional partial image areas by means of conventional, generally analogue but also digital interpolation methods. For example, the contours in the grey-value image of a one- or two-dimensional ultrasound recording are then compared with the contours of a neighbouring grey-value image and, based on a three-dimensional plane polygon e.g. of the third or fifth grade, linked together in order to “fill up” the missing data between the one- or two-dimensional partial image areas.
These conventional methods are time-consuming, require a lot of calculation work and are mostly not suitable for real-time methods, i.e. such methods where the physician for example wants to follow the progress of the operation in real time by means of an ultrasound during the operation itself.